Electric starter for small internal combustion engines

ABSTRACT

AN ELECTRIC MOTOR DRIVEN STARTER FOR A SMALL VERTICAL SHAFT INTERNAL COMBUSTION ENGINE. A STEEPLY PITCHED THREADED CONNECTED BETWEEN THE DRIVE SHAFT AND THE PINION THEREON EFFECTS RAPID RETURN MOTION OF THE PINION TOWARD ITS INACTIVE POSITION IN CONSEQUENCE OF THE ROTATION THEREOF IN THE SAME DIRECTION AS THE SHAFT IS DRIVEN, BUT AT A GREATER RATE. A COLLAR OF RESILIENTLY YIELDABLE MATERIAL DEFINES THE INACTIVE POSITION OF THE PINION AND CUSHIONS ITS RETURN THERETO. THE COLLAR ENCIRCLES A BEARING IN WHICH THE SHAFT IS JOURNALLED, AND IT IS NORMALLY FRICTIONALLY ENGAGED BY THE RETRACTED PINION AND SNUGLY CONFINED BETWEEN THE RETRACTED PINION AND A FIXED WALL IN WHICH THE BEARING IS MOUNTED TO ASSURE AGAINST ENTRY OF DIRT INTO THE BEARING.

Dec. 7, 1971 J. R. HARKNESS 3,525,071

ELECTRIC STARTER FOR SMALL INTERNAL COMBUSTION ENGINES Filed April 5, 1970 '33 55 1 35 J4 I I g; b I

Jasgvl; Hffarlrzws United States Patent 3 625,071 ELECTRIC STARTER FOR SMALL INTERNAL COMBUSTION ENGINES Joseph R. Harkness, Germantown, Wis., assignor t0 Briggs & Stratton Corporation, Wauwatosa, Wis. Filed Apr. 3, 1970, Ser. No. 25,473

Int. Cl. F 02n 11/00 US. Cl. 74-7 R Claims ABSTRACT OF THE DISCLOSURE An electric motor driven starter for a small vertical shaft internal combustion engine. A steeply pitched threaded connection between the drive shaft and the pinion thereon effects rapid return motion of the pinion toward its inactive position in consequence of rotation thereof in the same direction as the shaft is driven, but at a greater rate. A collar of resiliently yieldable material defines the inactive position of the pinion and cushions its return thereto. The collar encircles a bearing in which the shaft is journalled, and it is normally frictionally engaged by the retracted pinion and snugly confined between the retracted pinion and a fixed wall in which the bearing is mounted to assure against entry of dirt into the bearing.

BACKGROUND OF THE INVENTION This invention relates to electric motor driven starters for internal combustion engines, and it has more particular reference to starting mechanisms for small single cylinder engines which serve as the prime movers of garden tractors and tillers, rotary lawn mowers, snow blowers and the like. One example of such an electric starter for small internal combustion engines can be found in my copending application Ser. No. 800,386, filed Feb. 19, 1969, now Pat. No. 3,526,146.

Like that of my aforesaid copending application. the starter of this invention is also comprised of two cooperatively associated units. One of these units includes an electric motor, and the other is readily attachable to the motor unit and includes a Bendix type starter mechanism driven by the motor.

The mechanism embodies the usual steeply pitched screw threaded connection between the starter pinion and its drive shaft, by which rotation of the latter relative to the pinion effects translation of the pinion axially along the shaft from a defined retracted position to an operative position at which it meshes with a gear of an engine to be started.

In starter mechanisms of the type herein concerned, however, there is a tendency for the pinion to turn with its drive shaft during initial rotation of the latter, and thu remain in its retracted position instead of being advanced into mesh with the engine gear. There are two main reasons for such failure of the starter mechanism.

Because of the steep pitch of the screw threaded connection between .the pinion and its shaft, accumulations of dirt or other foreign matter on the screw threads frequently caused the pinion to stick to the shaft and hence turn therewith during initial rotation of the shaft.

The practice of defining the retracted position of the pinion by a stop shoulder formed directly on its drive shaft also frequently leads to sticking of the pinion and consequent failure thereof to be advanced out of its retracted position in response to initial rotation of the drive shaft. In that case, the pinion becomes jammed in its retracted position as a result of galling due to the hammer blow of the pinion upon its stop shoulder each time the starter is operated and the pinion is returned to its retracted position.

3,625,071 Patented Dec. 7, 1971 SUMMARY OF THE INVENTION The starter of my aforesaid application represented one approach to the problem of providing a starter mechanism featuring the simplicity, low cost and dependability so essential to any accessory intended for use on small single cylinder internal combustion engines. This invention concerns another such approach to that same problem, and its purpose is to achieve greater dependability and a significant further reduction in cost of manufacture, as a consequence of simplification of the mechanism of which the starter unit is comprised.

More particularly, this invention has as one of its objects the provision of an electric motor driven engine starter featuring an improved Bendix type starter mechanism wherein rapid return of the pinion to its inactive position along a steeply pitched threaded connection with the drive shaft is cushioned by an annular collar of resiliently yieldable material on the drive shaft, which collar is directly enga-geable by the pinion to not only define the inactive position thereof, but by reason of its frictional engagement with the pinion, to add to the inertia thereof and thus assure the desired advance of the pinion to its operative position as soon as the drive shaft begins to rotate, despite the presence of some dirt or other foreign matter on its screw threads.

It is a more specific purpose of the invention to provide pinion cushioning means such as referred to in the preceding object, wherein the drive shaft is journalled in a bearing sleeve that projects toward the pinion from a fixed supporting wall, and wherein the cushioning collar is mounted on the projecting portion of the sleeve and normally cooperates with said wall and with the pinion to prevent entry of dirt into the bushing.

Still another object of the invention resides in the provision of an improved Bendix type starter mechanism featuring a neoprene pinion cushioning collar which encircles the pinion drive shaft and is held in po ition by ribs on a protective shell in which the starter mechanism is partially enclosed.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawing, which exemplify the invention, it being understood that such changes in the specific apparatus disclosed herein may be made as come within the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a View partly in elevation and partly in section of an electric starter mechanism embodying this invention; and

FIG. 2 is a sectional view taken on the line 22 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the accompanying drawing, the numeral 3 generally designates an electric starting device for a small single cylinder vertical shaft internal combustion engine having a ring gear, such as indicated at 4, that rotates on a vertical axis.

The starter is comprised of two units mounted one on top of the other. The lower one is a power unit 5 (only a portion being shown) which comprises a permanent magnet electric motor 6 mounted within a housing 7. The upper unit is a Bendix type starter mechanism 9 which comprises a jackshaft 10 having a starter pinion 25 thereon. The jackshaft is driven from the motor 6 and it is partially enclosed within a shell 11 that covers the side of the mechanism remote from the ring gear 4. The two units are secured to an adapter 12 which is confined between them, and which provides an end bell type of closure for the upper end of the motor housing, fixed thereto in the usual way. The adapter has a side wall 13 which projects upwardly from a horizontal wall 14 and surrounds meshing gears 15 and 16 on the motor and jackshafts, respectively.

The shaft of the electric motor projects upwardly through and is rotatably supported in a bearing 17 in the horizontal Wall 14. The drive gear 15 is secured to its upper end. The upright wall 13 on the adapter provides a seat for a base 18 on the bottom of the shell 11 of the starter mechanism 9. The base is secured to the wall 13 by means of aplurality of screws 19.

The adapter 12 also serves to mount the starting mechanism on one side of a vertical shaft engine, with the open side of the shell 11 of the starter unit facing the engine to allow the exposed rim portion of the ring gear 4 to project thereinto. For this purpose, the adapter is formed with integral mounting lugs 20 and 20', which extend upwardly from the adapter at its side remote from the shell 11. Screws, not shown, which pass through the lugs 20-20 and thread into tapped holes in the engine, serve to secure the bracket thereto.

The base 18 of the starter unit 9, also hereinafter referred to as a fixed wall, cooperates with the adapter to provide a housing for the gears 15 and 16. In addition, the base and a portion of the shell 11 remote therefrom carry bearings 22 and 23, respectively, in which opposite end portions of the jackshaft 10 are rotatably journalled to support the shaft with its axis parallel to the motor shaft but offset therefrom in the direction of the mounting lugs 20-20.

The jackshaft 10, also herein referred to as a Bendix shaft, has the usual steeply pitched external threads 24 that mate with corresponding threads in the interior of the starter pinion 25. Hence, relative rotation between the pinion and the shaft can effect the desired axial advancing and retracting motion of the pinion, between limits defined by upper and lower stops 26 and 27, respectively, on the Bendix shaft. The lower stop 27 is seated on the top of the base 18, and it is normally confined between the base and the starter pinion when the latter is in its retracted position shown. The pinion is spaced a slight distance beneath the ring gear 4, when it is in its retracted position.

A nut 28 threaded on the Bendix shaft holds the upper stop 26 clamped against a shoulder on the shaft defined by the upper ends of the screw threads 24 thereon. The shoulder locates the stop with its lower surface facing the pinion 25 and substantially flush with the upper face of the ring gear.

The upper stop 26 can be of any desired construction, but it is here shown as comprising an annulus 30' of elastic material confined within a cup 31 by means of a washer 32 engaged under the nut 24. Hence, the upper stop serves to cushion upward advancing motion of the pinion into mesh with the ring gear, produced as a consequence of rotation of the Bendix drive shaft 10 relative to the pinion 25.

When the pinion is engaged with the upper stop 26, it drivingly connects the ring gear with the Bendix shaft 10 so that cranking torque can be then applied to the engine by the electric motor 6.

As soon as the engine starts, the pinion 25 is rotated by the ring gear 4 at a rate greater than that at which the Bendix shaft is driven by the motor. As a consequence, the pinion is rapidly propelled downwardly toward its retracted position, to forcefully collide with the lower stop 27. A spring 29 encircling the Bendix shaft and confined between the stop 26 and the pinion resists motion of the latter away from engagement with the lower stop. 7

According to this invention, the lower stop 27 is provided by a collar of neoprene or other suitable elastic or resiliently yieldable material that will serve to cffectively cushion retracting motion of the pinion. The lower stop also has two other important functions, namely that of supplying friction torque to aid the inherent inertia torque in drawing the pinion upward along the threads of the Bendix shaft, and of preventing dirt and other foreign matter from entering the bearing 22in which the lower end portion of the Bendix shaft is journalled.

It will be recalled that the lower bearing 22 is carried by the base 18, and it is in the form of a bushing or sleeve which projects upwardly from the base to have its outer end terminate just short of a shoulder 33 on the Bendix shaft. The shoulder 33 is located at the upper end of an enlarged shaft portion which is received within the bushing.

The cushioning collar 27 encircles and is seated upon the projecting upper end portion of the bushing 22; and its lower end is provided with a circumferential flange 34 which flatwise engages the top of the base 18.

The collar is held in this position by a pair of ribs 35 formed on the interior of the shell 11 at diametrically opposite sides thereof. The ribs embrace the collar and bear against the upper face of the collar flange 34 to hold the collar against axial movement away from the base and to in effect anchor the collar thereto.

When the pinion 25 is in its retracted position, it cooperates with the base and with the collar to completely close the space surrounding that portion of the bushing 'which projects upwardly from the base. Consequently, the collar prevents dirt and other foreign particles from contacting that part of the shaft which is below the pinion 25, and from gaining access to the interior of the bushing.

It should be noted that the collar 27 extends axially upwardly beyond the upper end of the bushing 22, and past the shaft shoulder 33. Hence, retracting motion of the pinion will be interrupted by the collar 27 before the pinion can collide with the shoulder 33. This is an important feature of the invention, for without it, the pinion would strike the shoulder a severe hammer blow every time the starter was operated, with the result that galling would occur to an extent suflicient to cause jamming of the pinion in its retracted position. Obviously, the starter would be rendered inoperative by such jamming, for the pinion would then rotate with the Bendix shaft upon energization of the electric motor 6, and thus could not be advanced out of its retracted position.

It is also of the essence of the invention, that with the construction illustrated, the spring 29 normally urges the pinion into engagement with the collar 27. Hence friction between the collar and pinion can add to the inertia of the pinion and assure the desired advance thereof into mesh with the ring gear so soon as driving torque is imparted to the Bendix shaft 10, even though dirt and other foreign matter may have accumulated on the screw threads of the latter to an extent that would otherwise cause the pinion to stick in its retracted position.

From the foregoing description, together with the accompanying drawing, it will be readily apparent to those skilled in the art that this invention provides an unusually simple starter mechanism for small internal combustion engines, which mechanism nevertheless features a resilient collar that cushions retraction of the starter pinion in a way that eliminates jamming thereof in its retracted position, facilitates movement of the pinion out of its retracted position during initial rotation of the Bendix shaft; and also affords protection for the bearing on which the collar is mounted.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims:

1. An engine starter of the type wherein a steeply pitched threaded connection between a drive shaft and a pinion thereon is operable upon rotation of the pinion in the same direction as the shaft but at a greater rate to effect rapid retracting motion of the pinion axially along the shaft toward an inactive position, characterized by:

(A) a supporting wall for said shaft, having a surface toward which the pinion moves during retraction thereof;

(B) bearing means carried by said wall, in which the drive shaft is journalled;

(C) and a resiliently yieldable collar encircling the drive shaft and seated upon said surface of the supporting wall, to define the inactive position of the pinion and cushion its retraction thereto.

2. The engine starter of claim 1, further characterized by means fixed with respect to said wall and interengaged with the collar to prevent bodily movement thereof relative to said wall.

3. The engine starter of claim 2, wherein said interengaging means comprises:

(A) a circumferential flange on the collar extending outwardly from its periphery;

(B) and rib means fixed with respect to said wall and engaged with the side of the flange remote from said wall to hold the collar against axial movement away from said surface of the wall.

4. The engine starter of claim 3, further characterized by:

(A) said wall surface being substantially flat and nor mal to the axis of the drive shaft;

(B) and said flange having a flat surface in contact with said wall surface.

5. The engine starter of claim 1, further charatcerized by:

(A) said bearing means comprising a bushing secured in said wall and having an end portion projecting therefrom toward the pinion;

(B) and said cushioning collar being mounted on said projecting end portion of the bushing, and being cooperable with the pinion in the inactive position thereof to prevent entry of dirt and other foreign matter into said bearing means.

6. The engine starter of claim 1, further characterized by:

(A) the drive shaft having one end portion journalled in said bearing means and having its opposite end portion spaced a distance from the pinion and at the side thereof remote from said wall;

(B) said wall comprising part of a shaft supporting structure having other bearing means thereon to rotatably journal said opposite end portion of the drive shaft;

(C) and said supporting structure further comprising a cup-like shell extending between and joining the bearing means for said opposite end portions of the shaft, said shell extending around only one side of the shaft.

7. The engine starter of claim 6, further characterized by:

(A) said shell having ribs extending along its interior and straddling opposite sides of the drive shaft near said wall; (B) and flange means on the collar confined between said ribs and said wall.

8. An engine starter of the type having a pinion which is normally held in a retracted position on a drive shaft but is propelled axially along the shaft between retracted and operative positions as a consequence of relative rotation between it and the drive shaft, characterized by:

(A) supporting structure for the drive shaft having a wall toward which the pinion moves during retraction thereof;

(B) a resiliently yieldable collar encircling the shaft;

(C) and means connecting the collar to the supporting structure with the collar adjacent and fixed with respect to said wall thereof and in position to be directly engaged by the pinion to define its retracted position and to cushion retracting motion thereof.

9. The engine starter of claim 8, wherein a spring acting on the pinion normally holds it frictionally engaged with said resiliently yieldable collar so that the collar resists turning of the pinion with the drive shaft and thus assures proper advance of the pinion out of its retracted position as soon as rotation is imparted to the drive shaft.

10. Engine starting mechanism, characterized by:

(A) a power unit comprising (1) an electric motor drive gear,

(2) and a motor housing having structure at one end thereof including a first wall member extending along one transverse side of the motor driven gear to isolate it from the remainder of the housing;

(B) a starter unit comprising (1) a jackshaft having a gear thereon meshing with the motor driven gear, and having a pinion threaded thereon and movable axially therealong in consequence of relative rotation between it and the jackshaft, toward and from an operative position at which it is constrained to rotate with the jackshaft,

(2) and shaft supporting structure having a base providing a second wall member extending along the opposite transverse side of the motor driven gear and fixed with respect to said first wall member;

(C) wall portions on said wall members cooperating therewith to define an enclosure for said meshing gears;

(D) lug means carried by one of said wall members and providing for securement of the starting mechanism to an engine;

(E) and a resiliently yieldable collar encircling the jackshaft and resting on said second wall, externally of said enclosure, to cushion motion of the pinion away from its operative position.

References Cited UNITED STATES PATENTS 2,509,361 5/1950 McCreary 747 UX MILTON KAUFMAN, Primary Examiner 

